There is a general trend towards miniaturisation of portable electronic devices, including portable wireless devices. As a result, antennas compete for space with the other device components (e.g. battery, display, keypad, printed circuit board).
In addition, modern wireless systems demand increasingly greater bandwidths in order to accommodate higher data rates. This is particularly true of video and audio applications that use the Ultra-Wideband (UWB) protocols being standardised by the IEEE. However, the goals of reduced physical size and increased bandwidth are not normally compatible. Further, reducing the physical size of the antenna normally tends to reduce the radiation efficiency of the antenna. There are fundamental theoretical performance compromises for electrically small antennas between required bandwidth, radiation efficiency and physical volume of the near-fields around the antenna (at a given centre frequency). Recent advances in small antenna design have attempted to achieve the highest bandwidth and radiation efficiency for a given volumetric size and operating frequency.
A key challenge in small antenna design is to provide adequate VSWR (voltage standing wave ratio) bandwidth and radiation performance for a given product application and physical volume requirement.
It would be desirable, therefore, to provide an antenna which, physically, is relatively small while satisfying relatively large bandwidth requirements and radiation efficiency requirements.
To this end, United States patent application US2005248488 (Modro), discloses a planar antenna folded to preserve or enhance the near-field resonant modes of the structure. It would be desirable, however, to improve on the antenna of US2005248488.